Applicant has already described in U.S. Pat. No. 4,214,378 a machine for drying and/or butt-jointing "green" or "non-green" wood veneer by continuous contact engagement, said veneer being fed by being unwound or sectioned and offered up in the direction of the wood grain or in a direction perpendicular thereto, in which machine an effective drying and jointing zone is defined and which comprises an input conveyor belt and an output conveyor belt, which are driven indepently and each constituted by upper and lower sets of endless chains with pallets or with blocks, these chains each comprising an active run and a return run and driven simultaneously by sprockets and running by roller means on supporting guide rails, their opposite active runs compressing and conveying the veneer, whilst their return runs are heated.
In accordance with the aforesaid patent, the shearing force, which is exerted beforehand in the transfer zone from one section to the next in machines with several consecutive sections, is advantageously distributed over the whole surface of the veneer and not on a single transverse line, due to the fact that the input and output conveyors are juxaposed contiguously in the effective drying and jointing zone of the machine, in the form of groups of active runs of alternating chains belonging to each of said conveyors, arranged in an even number of chains in one conveyor and an odd number of chains in the other conveyor, first pressure means being provided at the entrance to the effective zone, vertically above the chains of said input conveyor, and second pressure means arranged at the exit of the effective zone, vertically above the chains of said output conveyor, the input conveyor being driven at a higher speed than the output conveyor.
In the effective zone of this machine, the veneer is hence transported continuously between two movable layers of juxtaposed and contiguous chains, whose pallets or blocks form a flat united heating surface similar to a movable heating plate. The rollers of the active runs of the chains form the lower layer running on associated guide rails, whilst the active runs of the chains forming the upper layer are inverted, rollers upwards, and rest through their own weight on the veneer supported by the lower layer. Due to the fact that each active run of the upper layer is exactly superimposed on its homolog of the lower layer and advances at the same speed as the latter, the veneers are subjected to uniformly distributed pressure corresponding to the weight of the pallets or blocks and enabling in particular, drying by contact, or back-gluing, if the weight is sufficient.
However, Applicant has now realised that the pressure so-applied to the veneer could not be varied, since it is determined by only the weight of the pallets or blocks forming the upper layer, except, obviously, at the level of the input and output pressure devices of this machine according to the aforesaid patent.